1. Field of the Invention
The present invention relates to an electrophotographic or an electrostatic-recording image forming apparatus, and more particularly relates to an image forming apparatus such as a copier, a laser beam printer, or a facsimile that are capable of forming a visual image on an image bearing member and transferring the visual image on a transfer material to obtain an image.
2. Related Background Art
Image forming apparatuses such as electrophotographic copier and printer are equipped with a fixing unit that heats a toner image formed on a recording material (transfer material) for fixing. As the fixing unit is used repeatedly, a fixing roller may generate a flaw on the surface or a pressure roller may generate a wrinkle on the surface, and such a flaw or a wrinkle causes a failure in fixing or in image formation, and therefore a roller has to be replaced periodically.
Further, the fixing unit may have to be detachable and attachable so as to allow for a trouble in the fixing unit of the transfer material such as a paper jam due to some reasons, so as to remove the transfer material easily. To this end, the fixing unit is generally configured to allow a serviceman and a user to detach/attach it.
The fixing unit is further provided with a component to establish electrical connection with a main body of the image forming apparatus so as to feed electricity to a heater, a thermistor, and a thermo-switch therein. As such a component, a drawer connector is typically used.
When the fixing unit is attached to the main body of the apparatus, a fixing unit-side drawer connector provided in the fixing unit is fitted with a main body-side drawer connector in the apparatus main body for coupling. Then, connector terminals in the connectors in number corresponding to electrical connection required are brought into contact with each other, so as to establish electrical connection of the components such as the heater, the thermistor, and the thermo-switch. The draw connectors used for this purpose typically have many connection terminals to feed electricity to a plurality of components, thus often requiring a force to detach and attach it.
When an image forming apparatus includes a fixing unit that is detachable/attachable with respect to the apparatus main body, such an image forming apparatus is normally equipped with an attachment detection function enabling detection whether the fixing unit is attached or not to the apparatus main body. If an attachment detection judgment portion determines that the fixing unit is not attached, then an operation of the image forming apparatus is prohibited. To detect the attachment, electrical connection between the terminals in the above-stated connectors is detected, for example.
However, even when the above-stated connectors are inserted to predetermined positions of the apparatus main body, other portions of the fixing unit may not be inserted to their predetermined positions. Further, the above-stated drawer connectors that feed electricity to the fixing unit may not be inserted completely to the end physically even when the connector terminals between the fixing unit-side and the apparatus main body-side are electrically connected.
As one of the methods of detecting attachment of a fixing unit, Japanese Patent Application Laid-Open No. 2007-233306 discloses a method of detecting attachment at two positions in the longitudinal direction of a fixing unit. The technique disclosed detects an attachment state at the two positions so as to prevent an image forming apparatus from printing while the fixing unit being attached inclined with reference to the apparatus main body.
However, as described above, the drawer connectors that feed electricity to the fixing unit may not be inserted completely to the end physically even when the connector terminals between the fixing unit-side and the apparatus main body-side are electrically connected. Therefore, the disclosed technique cannot completely prevent the case where a printing operation is permitted even when the fixing unit is aligned obliquely with reference to the correct direction of the image forming apparatus main body. When the printing operation is performed while the fixing unit being aligned obliquely with reference to the correct direction of the image forming apparatus main body, there is a high possibility for a recording material to cause jam at the fixing unit portion.